"For 40 years, I put my body through a tremendous amount of work"

Lee Majors is describing the amount of physical labor he has done over the course of his life. He has worked hard for 40 years, pressing his body to its limits. This could imply that he has done a lot of manual work, such as building and construction work, or that he has been associated with a physically requiring profession such as acting or sports. It could also imply that he has actually been involved in a physically requiring pastime such as martial arts or weight-lifting. Whatever the case, it is clear that Lee Majors has put in a lot of effort and devotion to his physical health and well-being over the past 4 decades. He has pushed himself to the limitation and has achieved a lot of success in whatever he has done.